Partition Coefficient (Urgent)

Aug 2019
Hello all,

I am facing difficulties answering these questions. Any sort of help will be appreciated as my exams are really close!

1) Butanoic acid (pKa = 4.83) has a partition coefficient of 5.4 (favouring benzene) when distributed between water and benzene. Find the concentration of butanoic acid in each phase when 100 mL of 0.20M aqueous butanoic acid is extracted with 25 mL of benzene at pH 4.20

2)The acid HA (Ka = 4.2 x10-4) equilibrates between water (lower phase) and ether. i. Define the distribution coefficient (D) and partition coefficient (K) for this system. ii. Calculate D at pH 4.0 if K = 52. iii. Will D be greater or less at pH 3.50 than at pH 4.00?. iv. At what pH will D be unity (1). v. Calculate the fraction of HA remaining in the aqueous phase if 25.0 ml of an aqueous solution of 0.001M HA is extracted with two aliquots of 50.0 ml of ether

I can't even start to solve them as I lack basic understanding towards Partition Coefficient. Any help at all will be appreciated!